Device for providing a liquid additive

ABSTRACT

The invention relates to a device for providing a liquid additive, comprising at least one PTC heating element, which is designed to melt frozen liquid additive in the device; wherein the at least one PTC heating element of the device is held on both sides by a two-part heat-conducting structure, wherein a voltage source is connected to the two-part heat-conducting structure in such a way that electric current can be conducted from the one heat-conducting structure to a side of the PTC heating element and through the PTC heating element to the other heat-conducting structure on the other side of the PTC heating element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of PCT Application PCT/EP2015/062290, filed Jun. 2, 2015, which claims priority to German Application DE 10 2014 107 863.2, filed Jun. 4, 2014. The disclosures of the above applications are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a device for supplying a liquid additive.

BACKGROUND OF THE INVENTION

Devices for providing a liquid additive are used for example in the automotive field for supplying a liquid additive to an exhaust-gas treatment device for purification of the exhaust gases of an internal combustion engine of the motor vehicle. Exhaust-gas treatment devices in which a liquid additive is used for the purification of exhaust gases are widely used.

An exhaust-gas purification method particularly commonly implemented in such exhaust-gas treatment devices is the method of selective catalytic reduction (SCR method). In said method, nitrogen oxide compounds in the exhaust gas are reduced with the aid of a reducing agent. Here, ammonia is typically used as reducing agent. The exhaust-gas treatment device typically has an SCR catalytic converter on which the nitrogen oxide compounds in the exhaust gas are reduced with the aid of the ammonia. Ammonia is generally stored in motor vehicles not directly but rather in the form of a reducing agent precursor solution. The reducing agent precursor solution is a liquid additive. One reducing agent precursor solution which is particularly frequently used is urea-water solution. A 32.5% urea-water solution is available under the trade name AdBlue®.

Upon the start of operation of a device of said type, it is a problem that said liquid additives can freeze at low temperatures. The urea-water solution described above, for example, freezes at −11° C. Such low temperatures may be encountered in particular during a long standstill period of the motor vehicle. After a long standstill period, it may be the case that the liquid additive in the device has frozen completely. The device then initially cannot provide any liquid additive. It is known for devices for providing liquid additive to have a heating system for melting frozen liquid additive, such that a provision of liquid additive is possible promptly after a start of operation.

As heating means for such devices, PTC (positive temperature coefficient) heating elements are proposed in particular. PTC heating elements are electrical heating elements which are heated by an electrical current flowing through them. They have the additional characteristic that the electrical resistance for the current increases with rising temperature. It is thus achieved that the electrical current automatically decreases at high temperatures. As a result of the decrease of the electrical current, the heating power also decreases. This provides automatic protection of a PTC heating element against overheating.

In the case of said devices with PTC heating elements, inadequate dissipation of the heat from the PTC heating element is a problem, because the PTC heating element is heated up to a high temperature in a short time, and thereafter conducts only a low electrical current. Thus, in a short time, the heating power is limited in self-regulating fashion, such that the desired heating function is realized only to a small extent.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to solve or at least alleviate the technical problems highlighted in connection with the prior art. It is sought in particular to propose a particularly advantageous device having at least one PTC heating element.

These objects are achieved by means of a device according to the features of claim 1. Further advantageous refinements of the invention are specified in the dependent patent claims. The features specified individually in the patent claims may be combined with one another in any desired technologically meaningful way and may be supplemented by explanatory facts from the description, with further design variants of the invention being highlighted.

A device for providing a liquid additive is proposed, which device has at least one PTC heating element which is designed to melt frozen liquid additive in the device, wherein the at least one PTC heating element of the device is received, on both sides, by a two-part heat-conducting structure, wherein a voltage source is connected to the two-part heat-conducting structure such that electrical current can be conducted through the PTC heating element from one heat-conducting structure on one side of the PTC heating element to the heat-conducting structure on the other side of the PTC heating element.

The device is preferably inserted as an installation unit into a tank. The device preferably has a housing, and is arranged on the tank base of the tank. The device has, in particular, an intake point at which liquid additive (in particular urea-water solution) be extracted from the tank. Furthermore, the device preferably has a line connector to which a metering line for providing the liquid additive can be connected. Normally, a duct runs through the device from the intake point to the line connector. In the duct there is arranged a pump by means of which the liquid additive can be delivered. The device has multiple PTC heating elements. The PTC heating elements are connected by way of a heat-conducting structure to the housing of the tank. A starting volume of liquid additive is situated in the tank around the device. The PTC heating elements are designed to heat liquid additive in the starting volume through the housing of the device. For this purpose, the heat-conducting structure bears against the housing preferably over a large area, in order that the liquid in the tank can be heated by way of the at least one PTC heating element in an effective manner. The PTC heating elements (and normally also the pump of the device) are supplied with electrical current and an electrical voltage by a voltage source of the device via electrical conductors. Around the outside of the housing there is optionally also arranged a filter which delimits the starting volume between filter and housing and covers the intake point such that the liquid additive, as it is extracted from the tank, is filtered by means of the filter. Around the outside of the housing, and outside the filter, there is optionally arranged a further coarse filter, which may prevent damage to the filter. The liquid additive within the tank (outside the coarse filter) has a temperature. The temperature is an operating parameter of the device that may be taken into consideration in the execution of the method.

Of particular importance for the described device is the connection of the at least one PTC heating element of the device to a heat-conducting structure of the device.

The at least one PTC heating element of the device is received, on both sides, by a two-part heat-conducting structure, such that the heat from the PTC heating element is conducted to the housing and to the liquid additive in as effective a manner as possible.

A voltage source is preferably connected to the two-part heat-conducting structure via electrical conductors, such that the electrical current may be conducted through the PTC heating element from one heat-conducting structure on one side of the PTC heating element to the heat-conducting structure on the other side of the PTC heating element. The (two-part) heat-conducting structure thus forms, at least in sections, electrical conductors for the contacting of the at least one PTC heating element. By way of this arrangement of the electrical conductors, effective utilization of the PTC material of the PTC heating element is made possible, and at the same time, an effective dissipation of heat from the at least one PTC heating element is realized.

It is preferable if, furthermore, spacer elements are arranged between the two parts of the two-part heat-conducting structure, such that, firstly, the individual parts of the two-part heat-conducting structure, or the two heat-conducting structures, are electrically insulated with respect to one another, but secondly, a thermally conductive bridge exists between the two parts of the two-part heat-conducting structure or the two heat-conducting structures. The spacer elements thus ensure that the heat from the heat-conducting structure arranged on that side of the PTC heating element which is averted from the housing can also be dissipated to the housing.

The heat-conducting structure is preferably composed of metal, and very particularly preferably composed of aluminum, because aluminum exhibits high thermal conductivity and, at the same time, a low weight.

The device is advantageous if the spacer elements form a thermally conductive bridge between the two parts of the two-part heat-conducting structure.

In this way, a dissipation of heat from the at least one PTC heating element to both parts of the two-part heat-conducting structure is possible, wherein an exchange of heat can take place between the two parts of the heat-conducting structure. The exchange of heat permits an equalization of heat if the heat flows out of the two parts of the heat-conducting structure differ.

It is furthermore advantageous if the device has a housing which is inserted in a tank for the liquid additive, wherein the housing is free from liquid additive and the at least one PTC heating element and the two-part heat-conducting structure are situated in the housing. The housing is preferably insulated in liquid-tight fashion with respect to the tank.

The device is furthermore advantageous if the heat-conducting structure bears areally against the housing. A (first) part of the heat-conducting structure is preferably of areal form and bears against an inner surface of the wall of the housing of the device. The housing of the device is preferably of cylindrical form. The inner surface thus preferably forms an inner circumferential surface.

A (second) part of the heat-conducting structure is preferably likewise of areal form and bears against an upper wall of the housing of the device. The second part of the heat-conducting structure preferably has arm-like sections which, at least in sections, are formed parallel to the first part of the heat-conducting structure. PTC heating elements are arranged between the arm-like sections of the second part of the heat-conducting structure and the first part of the heat-conducting structure.

A release of heat to the housing is in this case possible both via the first part of the heat-conducting structure and via the second part of the heat-conducting structure. Depending on the fill level of the liquid additive in the tank, the upper wall of the housing is or is not wetted with liquid additive. A significant flow-off of heat via the second part of the heat-conducting structure is to be expected only when the upper wall is wetted with liquid additive. In order that the heat is always correctly distributed between the first part of the heat-conducting structure and the second part of the heat-conducting structure, heat-conductive connections are arranged between the first part of the heat-conducting structure and the second part of the heat-conducting structure. The heat-conductive connections may for example be spacer elements which are arranged adjacent to the PTC heating elements.

The device is furthermore advantageous if a pump is arranged in the housing, which pump is connected via a duct to an intake point and to a line connector, wherein liquid additive may be extracted from the tank at the intake point, and a metering line for providing the liquid additive may be connected to the line connector.

The housing is referred to as a “dry” housing, despite the fact that a pump is arranged therein, because, in the housing itself, the liquid additive does not circulate freely, and the housing is therefore dry. Within the housing, the liquid additive is conducted in the duct and in the pump.

Also proposed is a motor vehicle which has an internal combustion engine, an exhaust-gas treatment device for purification of the exhaust gases of the internal combustion engine, and a device according to the invention for providing a liquid additive for the exhaust-gas treatment device.

In the exhaust-gas treatment device there is preferably arranged an SCR catalytic converter by means of which the method of selective catalytic reduction can be carried out. The described device is preferably connected to a metering line. The metering line leads to a metering device by means of which the liquid additive may be supplied to the exhaust-gas treatment device. The metering device preferably has, for this purpose, a nozzle which finely atomizes the liquid additive in the exhaust-gas treatment device (if appropriate with the aid of a pressurized medium such as air) and/or an injector by means of which the liquid additive can be dosed. The injector may for example be a valve which is opened and closed electrically.

The invention and the technical field will be explained in more detail below on the basis of the figures. The figures show particularly preferred exemplary embodiments, to which the invention is however not restricted. In particular, it should be noted that the figures and in particular the illustrated proportions are merely schematic.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1: shows a motor vehicle having a device;

FIG. 2: shows a tank having a device,

FIG. 3: shows a connection of a PTC heating element to a heat-conducting structure,

FIG. 4: shows another view of the connection as per FIG. 3,

FIG. 5: shows a view into the housing of a device from below,

FIG. 6: is a three-dimensional illustration of a two-part heat-conducting structure, and

FIG. 7: shows a detail view of the tank from FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

FIG. 1 shows a motor vehicle 16 having an internal combustion engine 17 and having an exhaust-gas treatment device 18 for the purification of the exhaust gases 19 of the internal combustion engine 17. An SCR catalytic converter as exhaust-gas purification component 21 is provided in the exhaust-gas treatment device 18. Provided on the exhaust-gas treatment device 18 is a metering device 20 by means of which the liquid additive 3 can be supplied to the exhaust-gas purification component 21. Liquid additive 3 is supplied from a tank 23 to the metering device 20 via a metering line 22 by a device 2. The liquid additive 3 has a temperature 34, which is in this case marked by way of example in the tank 23. The device 2 is arranged in surroundings (e.g. in the vicinity of the fuel tank of the motor vehicle), wherein the surroundings have an ambient temperature 35, which is in this case marked by way of example outside the tank 23. In the device 2 there are arranged, inter alia, PTC heating elements (not shown here) which are connected via electrical conductors 4 to a voltage source 5. The device 2 is connected to a monitoring unit 15.

FIG. 2 shows, in a side view, a tank 23 into which a device 2, as an installation unit 9, has been inserted. The device 2 has a housing 26 and is arranged on the tank base 27 of the tank 23. The device 2 has an intake point 29 at which liquid additive 3 (in particular urea-water solution) can be extracted from the tank 23. Furthermore, the device 2 has a line connector 28 to which a metering line 22 for providing the liquid additive 3 can be connected. A duct 36 runs through the device 2 from the intake point 29 to the line connector 28. In the duct 36 there is arranged a pump 25 by means of which the liquid additive 3 can be delivered. The device 2 has multiple PTC heating elements 1. The PTC heating elements 1 are connected by way of a heat-conducting structure 24 to the housing 26 of the tank 23. A starting volume of liquid additive 3 is situated in the tank 23 around the device 2. The PTC heating elements 1 are designed to heat liquid additive 3 in the starting volume through the housing 26 of the device 2. The PTC heating elements 1 (and the pump 25) are supplied with electrical current 10 and an electrical voltage 31 by a voltage source 5 of the device 2 via electrical conductors 4. Around the outside of the housing 26 there is optionally also arranged a filter 30 which delimits the starting volume between filter 30 and housing 26 and covers the intake point 29 such that the liquid additive 3, as it is extracted from the tank 23, is filtered by means of the filter 30. Around the outside of the housing 26, and outside the filter 30, there is optionally arranged a further coarse filter 32, which may prevent damage to the filter 30. The liquid additive 3 within the tank 23 (outside the coarse filter 32) has a temperature 34, where the temperature 34 is an operating parameter 14 of the device 2 that can be taken into consideration in the execution of the method.

FIG. 3 shows an advantageous connection of a PTC heating element 1 to a heat-conducting structure 24. The illustration shows a wall section of the housing 26 of the device 2 in a view from above (cf. the side view in FIG. 2). A PTC heating element 1 is received, on both sides, by a two-part heat-conducting structure 24, such that the heat from the PTC heating element 1 is conducted to the housing 26 and to the liquid additive 3 in as effective a manner as possible. A voltage source 5 is connected via electrical conductors 4 to the two-part heat-conducting structure 24, such that the electrical current 10 is conducted through the PTC heating element 1 from one heat-conducting structure 24 on one side of the PTC heating element 1 to the heat-conducting structure 24 on the other side of the PTC heating element 1. By way of this arrangement of the electrical conductors 4, effective utilization of the PTC material of the PTC heating element 1 is made possible, and at the same time, an effective dissipation of heat is realized. Furthermore, the spacer elements 13 are arranged between the two-part heat-conducting structure 24, such that, firstly, the individual heat-conducting structures 24 are electrically insulated with respect to one another, but secondly, a thermally conductive bridge exists between the heat-conducting structures 24. The spacer elements 13 thus ensure that the heat from the heat-conducting structure 24 arranged on that side of the PTC heating element 1 which is averted from the housing 26 can also be dissipated to the housing 26.

FIG. 4 shows a side view of the connection as per FIG. 3 along the section line V indicated in FIG. 3. The heat-conducting structure 24 is arranged, in the vicinity of the housing 26, within the device 2. The housing 26 is connected to the tank base 27.

FIG. 5 shows a view into the housing 26 of a device 2 from below. A circumferential wall 6 of the housing 26 and an upper wall 7 of the housing 26 are correspondingly visible. A first part 8 of the heat-conducting structure 24 bears against the circumferential wall 6. A second part 9 of the heat-conducting structure bears against the upper wall 6. The second part 9 of the heat-conducting structure 24 has arms 10 which, at least in sections, run parallel to the first part 8 of the heat-conducting structure 24. PTC heating elements 1 are arranged between the arms 10 of the second part 9 and the first part 8. Furthermore, spacer elements 13 are arranged between the arms 10 of the second part 9 and the first part 8. Likewise indicated in FIG. 5 are a pump 25 of the device and a duct 36 via which the pump 25 draws in the liquid additive at an intake point 29.

FIG. 6 shows a three-dimensional view of the two-part heat-conducting structure 24 with a first part 8 and with a second part 9.

FIG. 7 shows a detailed view of the tank 23 from FIG. 2 with a device 1. Additionally to the disclosure of FIG. 4, it can be seen here that the heat-conducting structure 24 is of two-part form with a first part 8 and a second part 9.

The invention permits particularly advantageous operation of a device for providing liquid additive. In particular, functional testing of the heat-conducting connection of PTC heating elements 1 to heat-conducting structures 24 and/or housing 26 is possible. In this way, it can be detected whether possible amendments or repairs (possibly also a replacement of the device) are necessary.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

1. A device for providing a liquid additive, comprising: at least one PTC heating element which is designed to melt frozen liquid additive in the device; a two-part heat-conducting structure having a first part and a second part, the at least one PTC heating element being surrounded on at least two sides by the two-part heat-conducting structure; and a voltage source connected to the two-part heat-conducting structure; wherein electrical current is conducted through the at least one PTC heating element from the first part of the heat-conducting structure on one side of the PTC heating element to the second part of the heat-conducting structure on the other side of the PTC heating element.
 2. The device of claim 1, wherein the voltage source is connected to the two-part heat-conducting structure using electrical conductors.
 3. The device of claim 1, further comprising spacer elements arranged between the first part and the second part of the two-part heat-conducting structure, such that the first part and the second part of the two-part heat-conducting structure are electrically insulated with respect to one another.
 4. The device of claim 3, further comprising a thermally conductive bridge, wherein the spacer elements form the thermally conductive bridge between the first part and the second part of the two-part heat-conducting structure.
 5. The device of claim 1, further comprising: a tank; a housing which is inserted in the tank such that the housing is separate from liquid additive, and the at least one PTC heating element and the two-part heat-conducting structure are located in the housing.
 6. The device of claim 5, wherein the heat-conducting structure is positioned adjacent the housing.
 7. The device of claim 5, further comprising: a duct; an intake point; a metering line; and a pump arranged in the housing, such that the pump is connected to the intake point and a line connector using the duct; wherein liquid additive is extracted from the tank at the intake point, and transferred to the metering line using the line connector.
 8. The device of claim 1, further comprising: an internal combustion engine; and, an exhaust-gas treatment device for the purification of the exhaust gases of the internal combustion engine; wherein the device provides liquid additive for the exhaust-gas treatment device. 